What Foam to Use
There are several different categories of foam that you might be using for 3D foam signage. By and far the most common of these is EPS (expanded polystyrene) foam. Available in a range of densities and sizes, EPS foam tends to be the foam of choice both from a budget and a production point of view. From the point of view of budget, lower density EPS foams are by far the most affordable option. From the point of view of production, its availability in large blocks which can be directly placed on the CNC foam router or hot wire foam cutter means that large 3D objects can often be carved out of one or two blocks, reducing assembly time and maximizing the production efficiencies that come with automated foam carving. A second major category of foam is polyurethane foam. These foams, which are available in much higher densities than EPS foams also come in at a higher price point. Because they are available only in sheets, in order to create 3D objects you have to actually paste the sheets together into a block, carve the block and then seal and smooth all the layers together. Generally the cost of materials and labor to do this is unrealistic. For lettering however, depending on the required thickness, poly foams might be the better option if long term durability in environmental extremes is required, as these foams will last. The third category of foam, blue extruded foam, is useful only for short-term lettering, as it will curl and peel much sooner than EPS and poly foams. Therefore, depending on what type of a foam sign you are making, you will have to choose the best foam for the specific situation.